This invention relates to electrical connecting elements such as connectors for electrically connecting wiring or circuit boards with each other, and anisotropic conductive elements for interconnecting terminals, electrodes, etc. on flexible printed wiring or circuit boards such as flat cables and circuit boards, and a method of producing the same.
Heretofore, the prior art connectors for electrically connecting wiring boards with each other, for example have generally required mechanisms/members for mechanically fixing the connectors and the wiring boards and maintaining the boards connected as well as members for establishing the connection. Conventional connectors having such mechanical coupling means have been correspondingly complicated in structure, resulting in hampering the miniaturization and slimming-down. Japanese Patent Publication No. 7-220846 issued Aug. 18, 1995 discloses producing a connector by bonding a metallic thin sheet to an insulating cushioning material and laser-machining channels in the metallic thin sheet, followed by bending the assembly perpendicularly to the channel machining direction into a U-shape with the cushioning material facing inward. This required machining channels by laser on connectors one by one, rendering the manufacturing process cumbersome.
On the other hand, to take the conventional manufacturing of flexible printed wiring boards (FPC) by example, the process involves forming a required conductor pattern on a substrate (base film), followed by laying a covering over the conductor pattern to protect and insulate the latter. However, it required a dedicated adhesive to bond the covering to the substrate, and involved an additional step to apply the adhesive.
Accordingly, it is an object of this invention to provide an electrical connecting element which is easy to manufacture, and a method of producing the same.
Another of this invention is to provide an electrical connecting element which is of simple construction and allows for reduction in size and thickness, and a method of producing the same.
According to one aspect of this invention, a metallic thin film is formed on a mold having protrusions complementary in shape to a conductor pattern to be formed, and a transfer layer of adherent (or sticky) material or adhesive material is applied to the metallic thin film laid over the protrusions, followed by pulling the transfer layer apart from the mold so as to transfer the metallic thin film covering the protrusions onto the transfer layer to thereby form the conductor pattern on the transfer layer.
Alternatively, the transfer layer may be applied to one side surface of the substrate. The term xe2x80x9cadherent materialxe2x80x9d used herein refers to the material with which two objects will be bonded together in such a manner that they may be subsequently peeled apart at the joined surfaces while the term xe2x80x9cadhesive materialxe2x80x9d used herein refers to the material with which two objects will be bonded together in such a manner that they may be hardly peeled apart at the joined surfaces.
In an alternative embodiment, the metallic thin film may be of multilayer construction including a prime layer having a weak adhesion to the mold.
The electrical connecting element according to this invention comprises a substrate having a transfer layer of adherent material or adhesive material thereon, and a conductor pattern provided on the transfer layer. The conductor pattern is obtained by forming a metallic thin film on a mold having protrusions corresponding to the conductor pattern, adhering the substrate to the metallic thin film laid over the protrusions by means of the transfer layer, followed by pulling the substrate away from the mold so as to have the metallic thin film laid over the protrusions transferred onto the transfer layer to thereby form the conductor pattern thereon.
The connector for use as an electrical connecting element according to this invention for electrically connecting wiring boards with each other comprises a wiring element composed of a substrate having a transfer layer of adherent material or adhesive material applied to one side surface thereof, and a conductor pattern having a plurality of parallel conductor lines formed on the transfer layer. The conductor pattern is obtained by forming a metallic thin film on a mold having ridge-like protrusions corresponding to the array of the conductor lines, adhering the transfer layer side of the substrate to the metallic thin film laid over the protrusions, followed by pulling the substrate away from the mold so as to have the metallic thin film on the protrusions transferred onto the transfer layer to thereby form the conductor pattern thereon, wherein the conductor lines of the conductor pattern is in opposing contact with the respective wiring lines to be connected of the two wiring boards being connected to thereby establish connection between those wiring lines, the substrate being pressed against the two wiring boards such that those portions of the transfer layer between the adjacent conductor lines are adherently (or stickily) attached to the surfaces of the two wiring boards to form a mechanical bond.
In an alternative embodiment, the wiring element may be folded in two along a fold line extending in the direction of arrayal (transversely) of the conductor lines of the conductor pattern with the conductor pattern side facing outwardly to form a connector for use as an electrical connecting element. Preferably in this case, the wiring element is folded back by 180xc2x0 and a spacer or retainer member is sandwiched between the folded legs of the element so that the wiring element may be secured to the retainer member.
In an alternative embodiment, the connector for use as an electrical connecting element comprises two of the wiring element constructed according to this invention. The two wiring elements are bonded together with the conductor patterns of one halves of the respective wiring elements in opposing contact with each other by virtue of the transfer layers of the two wiring elements being adherently attached together while the substrates of the other halves of the respective elements have spacers affixed thereto on the side opposite from the side on which the respective conductor patterns are formed.
The flexible printed wiring board for use as an electrical connecting element according to this invention comprises a covering laid over the surface of the wiring element according to this invention on which the conductor pattern is formed, the covering being bonded to the element by means of the transfer layer.
The anisotropic conductive element for use as an electrical connecting element according to this invention comprises the wiring element according to this invention having a conductor pattern composed of a number of conductor lines arranged parallel to each other at a predetermined pitch, the thus constructed wiring element being cut orthogonally to the length of the conductor lines into strips, a plurality of which are in turn stacked one on another in vertical alignment with each other, the thus built-up strips being pressed together in the direction of stacking to be laminated together in one piece assembly.
A method of producing an anisotropic conductive element for use as an electrical connecting element according to this invention comprises the steps of providing a mold having a multiplicity of grooves formed in the surface thereof in a grid pattern and a multiplicity of protrusions, one extending from the top of each of the rectangular raised sections surrounded by the grooves; forming a metallic thin film on the mold having the protrusions; providing a transfer layer of adherent material or adhesive material having a release sheet applied on one side thereof and penetrating the protrusions of the mold into and through the transfer layer into abutment against the release sheet to thereby bring those portions of the metallic thin film covering the side surfaces of the protrusions and the surfaces of the rectangular raised sections into close contact with the adherent material or adhesive material; pulling the transfer layer together with the release sheet apart from the mold; then removing the release sheet from the transfer layer to complete an anisotropic conductive element having formed thereon a multiplicity of conductor patterns penetrated through and held by adherent material or adhesive material.